As a means of increasing the interior space of the passenger compartment of a vehicle, it is well known to lower the installation position of the seats of the vehicle as much as possible in order to increase head clearance. In order to lower the seat position, it is necessary to decrease the height of the seat with respect to the floor of the vehicle, i.e., the clearance between the seat and the floor should be minimized. However, a seat position adjusting mechanism for moving the seat forwards or backwards and fixing the seat in the desired position must be provided within the clearance between the seat and the floor.
A typical conventional seat position adjusting mechanism for a vehicle comprises a lower rail secured to the vehicle floor, an upper rail secured to the seat and slidably engaging the lower rail, a plurality of position adjusting holes formed in either the lower rail or the upper rail, a latch member on the other rail for engaging the hole, and a coil spring wound around the latch member so that the latch member is urged to engage the hole. Since the coil spring has a cylindrical shape as seen in elevation, the clearance required between the seat and the vehicle floor is limited by the diameter of this coil spring. There are limits to how much the winding diameter of the coil spring and the dimensions of the latch member can be decreased since they are required to hold the seat in the fixed position even against the forces due to collisions. Therefore, it is difficult to decrease the clearance between the seat and the vehicle floor on account of the existance of this seat position adjusting mechanism.
Furthermore, the latch member ordinarily has a laterally wide, rectangular cross-section so that a gap is formed in the vertical direction between the latch member and the coil spring even if the latch member engages with the coil spring in the horizontal direction. This can cause unpleasant frictional noises, buckling, or even failure of the connection between the coil spring and the latch member.
Therefore, it is an object of the present invention to provide a seat position adjusting mechanism for a vehicle which can overcome these drawbacks of the conventional art and be compact-sized so as to allow reduction of the clearance between the seat and the vehicle floor.